feat: add worlds and merge clock into spawn world

[rafa-martin]

Key points:

• Remove stale, broken worlds; consider forward-porting later.
• Consolidate the /clock bridge into the spawn world to prevent duplicate /clock messages in multi-robot setups.
• Pin the ros2_control version in repos.yaml for Humble.

Copilot description:
This pull request introduces significant enhancements to the robotnik_gazebo_ignition package, focusing on expanding simulation resources, improving launch and bridging scripts, and adding new models and worlds for Gazebo Ignition. The changes include the addition of new warehouse and charging station models, a script for spawning multiple robots, updates to launch files for better compatibility, and several documentation and configuration improvements.

Simulation Assets and Models:

• Added new warehouse models (gz_warehouse, warehouse_simple) with corresponding configuration and SDF files, expanding available simulation environments. [1] [2] [3] [4]
• Added a detailed charging station model (robotnik_charging_station) including SDF, material scripts, and configuration files. [1] [2] [3]
• Included a new lightweight world file (lightweight_scene.world) for simplified simulation scenarios.
• Removed the outdated willow_garage.world file.

Launch and Bridging Improvements:

• Added a script (multiple.sh) to automate spawning multiple robots in simulation with customizable parameters.
• Updated launch files to include the models directory in installation, fix world path defaults, and add a dedicated /clock bridge node for time synchronization between Gazebo and ROS 2. [1] [2] [3]
• Removed the /clock bridge from the dynamic bridge YAML generation, as it is now handled by a dedicated node.

Documentation and Configuration:

• Improved the package README with a clearer description.
• Updated the robotnik_simulation.humble.repos to use an earlier, compatible version of gz_ros2_control.
• Minor cleanup in launch scripts and package files. [1] [2] [3]

These changes collectively enhance the usability and flexibility of the simulation package, making it easier to test multiple robots and scenarios with richer environments and improved ROS-Gazebo integration.

[RomanRobotnik]

Good job!